The present invention relates to a high voltage generator for generating a DC high voltage by boosting an AC voltage supplied at a low voltage and then rectifying the boosted voltage.
A high voltage generator generally having a structure shown in FIG. 5 known as a conventional high voltage generation apparatus, which is used to supply a high voltage, e.g. 150 kV, to an X-ray tube for a medical X-ray diagnosis apparatus, for example.
A high voltage generator shown in FIG. 4 as a circuit diagram includes, as high voltage components, a high voltage transformer 101 connected to input terminals IN.sub.1, and IN.sub.2, a high voltage rectifier 102 connected to the high voltage transformer 101 and three-pole output terminals OUT.sub.1, and OUT.sub.2, and a filament heating transformer 103 connected to other input terminals IN.sub.3 -IN.sub.6 and the output terminal OUT.sub.2. With this arrangement, an AC low voltage, e.g. 200 V, supplied to the input terminals IN.sub.1 and IN.sub.2 is transformed to a DC high voltage, e.g. 150 kV, and is supplied between the anode and filament of an X-ray tube 105 from the output terminals OUT.sub.1, and OUT.sub.2 through three-core high voltage cables 104, 104. Further, two focusing filaments of the X-ray tube 105 are heated by an AC voltage taken out from the output terminal OUT.sub.2. The AC voltage supplied to the input terminals IN.sub.1, and IN.sub.2 may be made to a high frequency by an optional inverter or high frequency converter 121 and in this case, the size and weight of the high voltage transformer 101 itself can be reduced.
These high voltage components are assembled as shown in FIG. 5. That is, the high voltage components 101, 102 and 103 are supported by support members 107, 107, - - - 107 and are assembled and then accommodated in a vessel 108 made of iron. Then after the interior of the vessel 108 has been dried, insulation oil 109 is supplied to the vessel 108 to insulate between the respective components.
When, however, even a slight amount of dust, water and metal powder float in the insulation oil 109, a dielectric strength may be lowered due to the convection of the foreign substances. Thus, as shown in FIG. 5, in the conventional technology, barriers 110, 110, - - - 110 each composed of an insulation material board are disposed between the components to restrict the convection of the foreign substances.
The output terminals OUT.sub.1, and OUT.sub.2 are actually composed of high voltage receptacles 111, 111 as shown in FIG. 5. Although each of the high voltage receptacles 111 includes a high voltage electrode unit and a ground unit, a predetermined insulation distance is provided between the high voltage electrode unit and the ground unit to prevent the occurrence of creeping discharge.
Further, as shown in FIG. 5, the high voltage receptacles 111, 111, the terminal tables 112, 112, - - - 112, constituting the input terminals IN.sub.1,- - - IN.sub.6, and the like are mounted on an upper cover 113. Low voltage cables 114, 114, - - - 114 are mounted to the terminal tables 112, 112, - - - 112, respectively.
Nevertheless, in the high voltage generator of the conventional structure described above, when the barriers are formed, the inside structure or components of the vessel is made complex. A sufficient factor of safety cannot help being employed for the distance between the respective high voltage components, by taking the deterioration of the insulation oil into consideration, and as a result, the space between the high voltage components is increased. In the same way, the high voltage receptacle must have an insulation distance set by taking a sufficient factor of safety into consideration. For these reasons, the conventional high voltage generator having the arrangement to achieve a dielectric strength by the insulation oil has a problem of large size and complex structure as a whole generator.
In addition, in the case of the inverter type high voltage generator, in which pulses are controlled by a frequency-variable inverter circuit, a problem arises in that the size and weight of the high voltage transformer itself is reduced by using a high frequency, the dielectric strength of the insulation oil is the same, and thus, the reduction of the size and the weight is naturally limited to achieve a predetermined dielectric strength. Therefore, a problem also arises such that the generator must have a certain degree of size and weight, thus requiring an ensurance of a large insulation space.
Furthermore, when the conventional high voltage generator is used by being mounted on the support frame of an X-ray CT (cathode tube) apparatus and the like, the air tightness of the portion sealed to the insulation oil causes a problem due to the accelerated rotation speed produced when the support frame is rotated and there is a possibility that the dielectric strength is made insufficient by the mixture of air with the insulation oil leak. Furthermore, when the high voltage generator is mounted on such a moving support frame, the strength of a support member must be increased to cope with the heavy weight of the high voltage generator. In this viewpoint, a problem of increased size and weight of an entire system to be mounted on the support frame arises.
Still furthermore, since in the high voltage generator having the arrangement using the conventional insulation oil it is difficult to perfectly seal the insulation oil, it is usually designed to draw out a high voltage cable upwards.